Expose functionality to download buildpacks

build.go

@@ -737,15 +737,15 @@ func (c *Client) processBuildpacks(ctx context.Context, builderImage imgutil.Ima
 			order = appendBuildpackToOrder(order, mainBP.Descriptor().Info)
 		case buildpack.PackageLocator:
 			imageName := buildpack.ParsePackageLocator(bp)
-			mainBP, depBPs, err := extractPackagedBuildpacks(ctx, imageName, c.imageFetcher, publish, pullPolicy)
+			mainBP, depBPs, err := extractPackagedBuildpacks(ctx, imageName, c.imageFetcher, image.FetchOptions{Daemon: !publish, PullPolicy: pullPolicy})
 			if err != nil {
 				return fetchedBPs, order, errors.Wrapf(err, "creating from buildpackage %s", style.Symbol(bp))
 			}
 
 			fetchedBPs = append(append(fetchedBPs, mainBP), depBPs...)
 			order = appendBuildpackToOrder(order, mainBP.Descriptor().Info)
 		case buildpack.RegistryLocator:
-			registryCache, err := c.getRegistry(c.logger, registry)
+			registryCache, err := getRegistry(c.logger, registry)
 			if err != nil {
 				return fetchedBPs, order, errors.Wrapf(err, "invalid registry '%s'", registry)
 			}
@@ -755,7 +755,7 @@ func (c *Client) processBuildpacks(ctx context.Context, builderImage imgutil.Ima
 				return fetchedBPs, order, errors.Wrapf(err, "locating in registry %s", style.Symbol(bp))
 			}
 
-			mainBP, depBPs, err := extractPackagedBuildpacks(ctx, registryBp.Address, c.imageFetcher, publish, pullPolicy)
+			mainBP, depBPs, err := extractPackagedBuildpacks(ctx, registryBp.Address, c.imageFetcher, image.FetchOptions{Daemon: !publish, PullPolicy: pullPolicy})
 			if err != nil {
 				return fetchedBPs, order, errors.Wrapf(err, "extracting from registry %s", style.Symbol(bp))
 			}

buildpack_downloader.go

@@ -0,0 +1,111 @@
+package pack
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/pkg/errors"
+
+	"github.com/buildpacks/pack/config"
+	"github.com/buildpacks/pack/internal/buildpack"
+	"github.com/buildpacks/pack/internal/dist"
+	"github.com/buildpacks/pack/internal/image"
+	"github.com/buildpacks/pack/internal/paths"
+	"github.com/buildpacks/pack/internal/style"
+	"github.com/buildpacks/pack/logging"
+)
+
+type buildpackDownloader struct {
+	logger       logging.Logger
+	imageFetcher ImageFetcher
+	downloader   Downloader
+}
+
+func NewBuildpackDownloader(logger logging.Logger, imageFetcher ImageFetcher, downloader Downloader) *buildpackDownloader { //nolint:golint,gosimple
+	return &buildpackDownloader{
+		logger:       logger,
+		imageFetcher: imageFetcher,
+		downloader:   downloader,
+	}
+}
+
+type BuildpackDownloadOptions struct {
+	// Buildpack registry name. Defines where all registry buildpacks will be pulled from.
+	RegistryName string
+
+	// The base directory to use to resolve relative assets
+	RelativeBaseDir string
+
+	// The OS of the builder image
+	ImageOS string
+
+	// Deprecated, the older alternative to buildpack URI
+	ImageName string
+
+	Daemon bool
+
+	PullPolicy config.PullPolicy
+}
+
+func (c *buildpackDownloader) Download(ctx context.Context, buildpackURI string, opts BuildpackDownloadOptions) (dist.Buildpack, []dist.Buildpack, error) {
+	var err error
+	var locatorType buildpack.LocatorType
+	if buildpackURI == "" && opts.ImageName != "" {
+		c.logger.Warn("The 'image' key is deprecated. Use 'uri=\"docker://...\"' instead.")
+		buildpackURI = opts.ImageName
+		locatorType = buildpack.PackageLocator
+	} else {
+		locatorType, err = buildpack.GetLocatorType(buildpackURI, opts.RelativeBaseDir, []dist.BuildpackInfo{})
+		if err != nil {
+			return nil, nil, err
+		}
+	}
+
+	var mainBP dist.Buildpack
+	var depBPs []dist.Buildpack
+	switch locatorType {
+	case buildpack.PackageLocator:
+		imageName := buildpack.ParsePackageLocator(buildpackURI)
+		c.logger.Debugf("Downloading buildpack from image: %s", style.Symbol(imageName))
+		mainBP, depBPs, err = extractPackagedBuildpacks(ctx, imageName, c.imageFetcher, image.FetchOptions{Daemon: opts.Daemon, PullPolicy: opts.PullPolicy})
+		if err != nil {
+			return nil, nil, errors.Wrapf(err, "extracting from registry %s", style.Symbol(buildpackURI))
+		}
+	case buildpack.RegistryLocator:
+		c.logger.Debugf("Downloading buildpack from registry: %s", style.Symbol(buildpackURI))
+		registryCache, err := getRegistry(c.logger, opts.RegistryName)
+		if err != nil {
+			return nil, nil, errors.Wrapf(err, "invalid registry '%s'", opts.RegistryName)
+		}
+
+		registryBp, err := registryCache.LocateBuildpack(buildpackURI)
+		if err != nil {
+			return nil, nil, errors.Wrapf(err, "locating in registry %s", style.Symbol(buildpackURI))
+		}
+
+		mainBP, depBPs, err = extractPackagedBuildpacks(ctx, registryBp.Address, c.imageFetcher, image.FetchOptions{Daemon: opts.Daemon, PullPolicy: opts.PullPolicy})
+		if err != nil {
+			return nil, nil, errors.Wrapf(err, "extracting from registry %s", style.Symbol(buildpackURI))
+		}
+	case buildpack.URILocator:
+		buildpackURI, err = paths.FilePathToURI(buildpackURI, opts.RelativeBaseDir)
+		if err != nil {
+			return nil, nil, errors.Wrapf(err, "making absolute: %s", style.Symbol(buildpackURI))
+		}
+
+		c.logger.Debugf("Downloading buildpack from URI: %s", style.Symbol(buildpackURI))
+
+		blob, err := c.downloader.Download(ctx, buildpackURI)
+		if err != nil {
+			return nil, nil, errors.Wrapf(err, "downloading buildpack from %s", style.Symbol(buildpackURI))
+		}
+
+		mainBP, depBPs, err = decomposeBuildpack(blob, opts.ImageOS)
+		if err != nil {
+			return nil, nil, errors.Wrapf(err, "extracting from %s", style.Symbol(buildpackURI))
+		}
+	default:
+		return nil, nil, fmt.Errorf("error reading %s: invalid locator: %s", buildpackURI, locatorType)
+	}
+	return mainBP, depBPs, nil
+}